Highly selective chelating resins and monomers for their preparation

ABSTRACT

Described are preferred monomers including a vinylbenzyl moiety N-bonded to an alkylaminopyridinyl or pyridylimidazolyl function. Also described are preferred acid salts of such monomers. Additionally, preferred processes involving and resins formed from these preferred monomers are described. The preferred resins are highly selective for valuable heavy metal ions such as copper and demonstrate superior iron rejection values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 07/750,467, filedAug. 20, 1991, now U.S. Pat. No. 5,180,822.

Which is a continuation-in-part of U.S. application Ser. No. 609,393filed Nov. 5, 1990, now U.S. Pat. No. 5,147,954, which is a divisionalof U.S. patent application Ser. No. 352,980 filed May 17, 1989, nowissued U.S. Pat. No. 4,968,806 which is hereby incorporated herein byreference in its entirety, which is a continuation-in-part of U.S.patent application Ser. No. 247,152 filed Sep. 21, 1988, now issued U.S.Pat. No. 5,015,706.

BACKGROUND OF THE INVENTION

The instant invention relates generally to chelating resins, and inparticular to highly selective chelating resins having alkylaminopyridylor pyridylimidazolyl functions, and to monomers for their preparation.

As background, polymer resins having ion-exchange properties have longbeen used to recover metal ions from solution. This recovery techniqueis advantageous because the resin insolubility and existence as asolid-phase material minimizes any contamination to the treated solutioncaused by the recovery process. Further, these chelating resins areoften suitable for removing metal ions from solutions too dilute forpracticable liquid-liquid extractions.

One resin attribute of great interest has been selectivity forparticular metal ions. Desirable chelating resins preferentially bindvaluable metal ions (e.g. copper and nickel) over less valuable metalsions (e.g. iron) at acid pHs (e.g. pHs of 1-4) which most often prevailin hydrometalurgical recovery operations. In this regard, certain resinsincorporating alkylaminopyridyl, imidazolyl or pyridylimidazolylfunctions have been reported to selectively bind these valuable metalions.

For instance, U.S. Pat. No. 4,202,944 to Hancock et al. describes resinswhich incorporate pyridyl, imidazolyl or imidazoline groups. Thedescribed resins are prepared by treating a preformed chloromethylatedpolystyrene matrix with a solution containing the active species ofinterest. The active species are thereby attached to thechloromethylated polystyrene matrix. Similarly, U.S. Pat. No. 4,031,038to Grinstead et al. describes chelate-exchange resins capable ofselective recovery of copper, nickel, and other valuable metals fromacidic aqueous leachate liquor. Again, the resins are prepared bysubsequently treating preformed chloromethylated styrene-divinylbenzenecopolymer beads, this time with an aminomethylpyridine species.

Resin preparations with chloromethylated polystyrene have beenextensively reviewed. See, "Chemical Transformations of ChloromethylatedPolystyrene", J. Macromol. Sci.--Rev. Macromol. Chem. Phys., 28, 503-592(1988); "Chloromethylstyrene: Synthesis, Polymerization,Transformations, Applications", J. Macromol Sci.--Rev. Macromol. Chem.Phys., 22, 343-407 (1982-83). As these reviews and the above-describedpatents demonstrate, by far, the predominant preparative approach in theliterature and industry has been to react preformed chloromethylatedpolystyrene beads with a solution of the ligand of interest. In onlyrelatively few instances, monomers incorporating the species of interesthave been prepared and polymerized. This approach has seemingly beendiscarded in many instances, possibly due to difficulties encountered inpreparing monomers of sufficient purity to give superior polymerproducts. For example, distillation, by far the most commonly usedpurifying method, has not been found to reliably purify monomersincorporating complicated ligands of interest. See, for instance, M.Tomoi, Y. Akada and H. Kakuichi, Macromol. Chem., Rapid Commun., 3,537-42 (1982). As such, the monomers will contain substantialimpurities, as will the polymers derived from them. This can severelyimpact selectivity of the polymers.

While efforts in the art and industry have provided chelating resinsdemonstrating some selectivity for certain valuable metals, the primarypreparative method has been attachment of ligands to preformedchloromethylated polymer beads. As the applicants' own experience hasshown, however, polymers prepared in this fashion have severaldisadvantages. For instance, the ligand attachment reaction very oftengives rise to undesirable byproduct ligands irreversibly attached to theresin which can diminish selectivity. In light of the foregoing, thereremains a need and demand for highly selective chelating resins, and tomonomers and methods for their preparation. It is this need to which theinvention described herein is addressed.

SUMMARY OF THE INVENTION

Accordingly, this invention provides in one preferred embodiment apolymerizable monomer for preparing a selective chelating resin, havingthe general formula I or II: ##STR1## wherein R¹ =(CH₂)_(n) -Py wheren=1 to 3 and Py=a pyridyl group; R² =H, a C₁ to C₁₂ alkyl group or,independently, another group of the formula R¹ ; and R³ =a pyridylgroup. These preferred polymerizable monomers have been prepared insubstantially pure form, preferably free from decomposition productsoccurring from distillation, and have proven to be highly valuablematerials enabling direct preparation of chelating resins having highselectivity for valuable metal ions in solution. Further, acid additionsalts of the preferred monomers have proven to be unexpectedly stableand accordingly constitute another preferred embodiment of theinvention.

Another preferred embodiment of this invention relates to a process forproducing a chelating resin. This process comprises a polymerizationincluding a preferred monomer as described above.

Another preferred embodiment of the invention includes a chelating resinhaving repeating units derived from a polymerizable monomer as describedabove.

These preferred embodiments provide highly valuable materials andprocesses demonstrating unexpected properties, and are or can be used toprepare extraordinarily selective metal chelating resins. Additionalobjects and advantages of the invention will become apparent uponreviewing the following description and appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to certain embodiments andspecific language will beused to describe the same. It will neverthelessbe understood that no limitation of the scope of the invention isthereby intended, such alterations, further modifications andapplications of the principles of the invention as described hereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

As indicated above, one preferred embodiment of this invention relatesto a polymerizable monomer for preparing a selective chelating resin.Generally, monomers of the invention include a vinylbenzyl moiety Nbonded to an alkylaminopyridyl function (e.g. --(CH₂)_(n) --Py offormula I) or a pyridylimidazolyl function (e.g. formula II).

As previously set forth, the preferred alkylaminopyridyl function R¹(and optionally R²) has the formula --(CH₂)_(n) -- Py wherein n=aninteger from 1 to 3, and Py is a pyridyl group, e.g. a 2-, 3- or4-pyridyl group, more preferably 2-pyridyl. Further, n is preferably 1(i.e. a methylene group is provided). As such, more preferred monomersof the invention include N-vinylbenzyl-N-2-picolylamine derivatives, forinstance N-vinylbenzyl-N-2-picolylamine itself (i.e. R¹ =--CH₂ --Pywhere Py is 2-pyridyl, and R² =H). R², as stated, can, independently, beanother group of the formula R¹. Especially preferred are monomers whereR¹ and R² are identical, e.g. as in the case ofN-vinylbenzyl-N-(bis)2-picolylamine. Additional preferred monomersresult where R² is an alkyl group, preferably a C₁ to C12 alkyl, whichcan be unsubstituted or substituted with groups that do notdetrimentally interfere with polymerization or with selectivity of thefinal resin. For instance, the alkyl group can be a hydroxyalkyl groupsuch as 2-hydroxyethyl or 2-hydroxypropyl. Accordingly, additionalpreferred monomers includeN-vinylbenzyl-N-2-hydroxyethyl-N-2-picolylamine andN-vinylbenzyl-N-2-hydroxypropyl-N-2-picolylamine.

As stated, additional preferred monomers occur within formula II, i.e.where a pyridylimidazolyl function is included. In the preferredmonomers these pyridylimidazolyl functions are N-bonded to thevinylbenzyl moiety at the 1 position of the imidazolyl ring. Thepyridylimidazolyl function is desirably a 2-pyridylimidazolyl function,for example as occurs in the preferred monomer1-vinylbenzyl-2-(2-pyridyl)imidazole.

As those skilled in the art will recognize and appreciate, the ringsystems present in the preferred monomers can be substituted withadditional noninterfering groups (e.g. alkyl, etc.) which do notdetrimentally affect the function of the monomers or the polymersderived from them. Such modifications are contemplated as providingmonomers and polymers of equivalent nature and function and aretherefore within the spirit and scope of the present invention.

The preferred monomers can be prepared by first reacting a hydride,hydroxide or alkoxide salt, e.g. sodium hydride, potassium hydroxide orsodium ethoxide, with a compound of the formula ##STR2## where R¹, R²and R³ are as previously defined, to thereby form the correspondingNa⁺ - NR¹ R² or ##STR3## salt. This salt is then reacted withvinylbenzyl chloride to form the desired monomer, which can then beconventionally filtered to remove inorganics, and concentrated. Also,where R² =H in the monomer product, this product can be further reactedwith a functionalizing agent, e.g. an epoxy compound such as ethylene orpropylene oxide, to thereby functionalize (e.g. hydroxyalkylate in thecase of epoxides) at the R² position.

In a preferred preparative process and further inventive embodiment, themonomer, once formed, is treated with an acid sufficiently strong toform an acid salt of the monomer. This acid addition salt is thenpurified by extraction into an aqueous layer, and optionally washed withtoluene to remove neutral water insoluble impurities. Afterpurification, the monomer can be converted back to free base formimmediately or after storage by treatment with a basic substance, e.g.aqueous ammonia, and is preferably extracted at least once with a polarorganic solvent such as methylene chloride. The resulting monomer hassuperior purity and is free from decomposition products occurring fromdistillation.

The acid salt form monomer demonstrates surprising improved stabilityagainst polymerization, both in solution and when isolated as a solidmaterial. For instance, as illustrated in Example 11, when stored underrefrigeration in free base form, monomers of the invention form dark,tarry material and are greater than 50% lost over a period of about 2months, and further have proven unusable for the preferredpolymerization procedures. On the other hand, acid salts of the monomersstored over similar periods in their solid form are essentially 100%retained, and in solution are at least 75% retained. Importantly, whenconverted back to free base form, the monomers stored as acid saltsyield material which can be successfully polymerized to form thepreferred selective chelating resins. These acid salt form monomers thuscan be reliably stored and also constitute a further preferredembodiment of the invention. As to specific acids which can be used toprepare the preferred acid salt-form monomers, these include forinstance hydrochloric, sulfuric, hydrobromic, methanesulfonic, formicand phosphoric acid although others will be suitable as those skilled inthe area will appreciate.

In preferred work to date, the inventive monomers have been suspensioncopolymerized with at least one comonomer to provide a suitablecrosslinked polymer matrix. For instance, it has proven highly desirableto suspension copolymerize the inventive monomer with styrene anddivinylbenzene comonomers. The organic phase for the polymerizationdesirably contains divinylbenzene, styrene, the inventive monomer and asuitable polymerization catalyst, e.g. Vazo 52 available from E.I. duPont de Nemours & Co., Inc. of Wilmington, Del., U.S.A. The monomers aretypically included in ratios of about 2 to 30 weight % divinylbenzene:5to 45 weight % styrene:30 to 65 weight % inventive monomer. Moredesirably, the inventive monomer comprises at least 50 weight % of themonomers to be polymerized. The preferred aqueous phase has been a 0.2%solution of Methocel 50-123, a material commercially available from DowChemical Co. of Midland Mich., U.S.A., although other aqueous phaseswill of course be suitable and their utilization well within the purviewof those practiced in the field.

The resulting resins can be gel or macroreticular form, preferablybeads, and demonstrate superior selectivities and affinities for forcopper and other valuable metal ions. The resins of the invention alsohave excellent iron rejection values and thus provide superior selectiveand cost-effective recovery of valuable metal ions in many applications.

As to recovering the copper or other metal from the resin, this can beconventionally accomplished by elution with a strong acid such assulfuric or hydrochloric acid. The resins can then be used directly inanother metal recovery, or optionally can be regenerated by treatmentwith an aqueous base (NaOH, NH₃, etc.) prior to use in a subsequent run.As another example, copper ions can also be selectively removed withaqueous ammonia.

For the purposes of promoting a further understanding of the inventionthe following examples are provided. It will be understood that theseexamples are illustrative and are not intended to be restrictive of theinvention.

EXAMPLE 1 Preparation of N-Vinylbenzyl-N-(bis)2-picolylamine

Sodium hydride was initially washed with hexane to remove mineral oil.The hexane-wet solid contained 60% sodium hydride. Twenty-eight grams(0.694 mole) of the wet hydride were combined with 300 mL of anhydrousTHF in a previously dried round bottom flask fitted with stirrer,thermometer, nitrogen inlet and a reflux condenser. Bis-2-picolylamine(112.6 g, 0.565 mole) was added and the resulting mixture stirred forthree hours. During this time the reaction temperature rose to 40° C.and H₂ was evolved. After three hours the reaction temperature hadreturned to 25° C. and a solution containing 98.6 g of vinylbenzylchloride (0.564 mole) in 75 mL of THF was added dropwise while thereaction temperature was maintained between 30°-40° C. with cooling.When the addition of vinyl benzyl chloride solution was complete, thereaction mixture was stirred for 20 hours at room temperature under anitrogen purge. The reaction mixture was then filtered and concentratedat reduced pressure to give 174 g of theN-vinylbenzyl-N-(bis)2-picolylamine monomer.

EXAMPLE 2 Preparation of N-Vinylbenzyl-N-(bis)2-picolylamine via AcidSalt

Bis-2-picolylamine (79.7 g, 0.4 mole), sodium hydride (80 wt. % in oil,14.9 g, 0.5 mole), and anhydrous THF (250 mL) were combined withstirring in a dry, nitrogen-purged round bottom flask. Stirring wascontinued until no more heat or hydrogen were evolved and toluene (600mL) was added. The majority of the THF was removed from the mixture bydistillation and the reaction mixture cooled to room temperature.Commercial vinylbenzyl chloride (63.6 g) was added slowly and thereaction maintained below 40° C. for 6.hours. Unreacted sodium hydridewas quenched with water and carbon dioxide and the reaction mixturefiltered to remove sodium chloride.

With cooling, keeping the temperature below 40° C., 10 wt. %hydrochloric acid (115 mL) was added to the filtrate. The aqueous layercontaining the monomer was separated, washed with toluene. The originaltoluene layer was washed with two 100 mL portions of water and all waterlayers combined. The pH of the aqueous solution was adjusted to 9.0 withaqueous ammonia. The monomer was extracted with three 100 mL portions ofmethylene chloride and the combined organic layers concentrated atreduced pressure to give 113.5 grams of the Bis-2-picolylamine monomer.

EXAMPLE 3 Further Preparation of N-Vinylbenzyl-N-(bis)2-picolylamine

Potassium hydroxide (85%, 29.4 g, 0.446 mole) and acetonitrile (200 mL)were combined and heated to reflux for 30 minutes. The mixture wascooled to room temperature and Bis-2-picolylamine (79,8 g, 0.4 mole) wasadded to give a purple solution that changed to brown.Vinylbenzylchloride (96%, 63.6 g, 0.4 mole) was added dropwise duringfifteen minutes with stirring and cooling to hold the reactiontemperature at 45° C. or less for 18 hours, solvent was removed atreduced pressure and the resulting residue dissolved in toluene (200mL). The toluene solution was first washed with two portions of water(200 mL) and then extracted with aqueous acid (75 mL of concentrated HCldiluted with 200 mL of water). The acid layer was separated, treatedwith aqueous ammonia (100 mL) until basic, and extracted with methylenechloride (100 mL) and cyclohexane (200 mL). The extracts were combined,dried over anhydrous magnesium sulfate, and concentrated at reducedpressure to give 129.8 g of the title monomer containing less than 2% ofunreacted Bis-2-picolylamine.

EXAMPLE 4 Preparation of N-Vinylbenzyl-N-2-picolylamine

The procedure described in Example 1 above was carried out with 43.3 g(0.4 mole) of 2-picolylamine substituted for the bis-2-picolylamine.Concentration of the methylene chloride gave 82.5 g of theN-vinylbenzyl-N-2-picolylamine monomer.

EXAMPLE 5 Preparation of 1-Vinylbenzyl-2-(2-pyridyl)imidazole

Step (a)--preparation of 2-(2-pyridyl)imidazole: Generally, theprocedure described in U.S. Pat. No. 4,202,944 was used to prepare2-(2-pyridyl)-imidazole. Accordingly, with stirring and cooling, chilledsolutions containing 14.9 g of 2-pyridylaldehyde in 14.5 mL of ethanoland 30 mL of 30% aqueous glyoxal solution in 15 mL of ethanol werecombined. Immediately and with continued cooling, 40 mL of cold 2.0Naqueous ammonia were added. The reaction mixture was stirred for 1 hourat 0° to 2° C. and then at room temperature for 17 hours. Solvent wasremoved at reduced pressure and the residue extracted with 5×30 mLportions of diethyl ether. The ether extracts were combined and afterestablishing the absence of peroxides, concentrated and distilled togive 9.7 g of 2-(2-pyridylimidazole) as an oil that solidified uponcooling.

Step (b)--reaction with vinylbenzyl chloride--Using the procedure inExample 1, 82.0 g (0.567 mole) of 2-(2-pyridylimidazole) were reactedwith 99.1 g (0.567 mole) of vinylbenzyl chloride to give 141.0 g of thepyridylimidazole monomer. The reaction can also be carried out usingsodium ethoxide instead of sodium hydride.

EXAMPLE 6 Preparation of N-Vinylbenzyl-N-2-picolyl-N-2-hydroxyethylamine

To a stirred solution containing 134.6 g (0.6 mole) of the2-picolylamine substituted monomer of Example 4 in 300 mL oftetrahydrofuran were added dropwise 27.3 g (0.62 mole) of ethylene oxideover a 2 hour period. The reaction mixture was allowed to stir at roomtemperature for 20 hours and the solvent removed at reduced pressure togive 153.0 g of the hydroxyethylamine substituted monomer. Thisprocedure is repeated, except substituting propylene oxide for theethylene oxide, to provide the corresponding hydroxypropylaminesubstituted monomer.

EXAMPLE 7 Preparation of Aqueous and Organic Phases for Polymerization

A 1.7% solution of METHOCEL 50-123 was prepared according to themanufacturer's instructions by dispersing the solid in water, withvigorous stirring, at about 85° C. and then adding ice to rapidly coolthe mixture. For the reactions described below, this solution wasdiluted to give a 0.17% solution of METHOCEL 50-123. Organic phases wereprepared containing 55% divinylbenzene, styrene, and amine substitutedmonomer, and a catalyst, Vazo 52.

EXAMPLE 8 Polymerization Including N-Vinylbenzyl-N-2-picolylamine

One hundred and sixty milliliters of the 0.17% METHOCEL 50-123 wereheated to 55° C. under a nitrogen purge in a round-bottom flask fittedwith a thermometer and stirrer. A monomer solution containing 1.2 g of55% divinylbenzene, 6.9 g of styrene, 9.96 g of the monomer prepared inExample 4, and 0.1 g of Vazo 52 was added to the stirred aqueoussolution in one portion below the liquid level. The reaction temperaturewas maintained at 55° C. for 3 hours and then increased to 80° C. whereit was held for 18 hours. The resulting slurry was cooled, and theproduct orange beads were filtered and rinsed with water and methanol,and dried.

EXAMPLE 9 Polymerization Including N-Vinylbenzyl-N-(bis)2-picolylamine

The procedure of Example 8 was used to polymerize a mixture containing1.2 grams of 55% divinylbenzene, 6.9 grams of styrene, 14.05 grams ofthe monomer of Example 2, and 0.1 g of Vazo 52. A light tan polymerresulted.

EXAMPLE 10 Polymerization Including 1-Vinylbenzyl-2-(2-pyridyl)imidazole

The polymerization method described in Example 8 above was used topolymerize an organic mixture containing 1.2 g of 55% divinylbenzene,6.9 g of styrene, 11.3 g of the monomer prepared in Example 5, and 0.1gof Vazo 52. Hard, light yellow beads of uniform size were obtained.

EXAMPLE 11 Stability of Free Base Monomers vs. Acid Salt Counterparts

The monomer preparation described in Example 2 was repeated with thefollowing changes. After reaction of the sodium hydride adduct ofbis-2-picolylamine with vinylbenzyl chloride, a majority of the THF wasremoved as before and the reaction mixture cooled. The unreacted sodiumhydride was quenched with carbon dioxide and a minimum of water and themixture filtered as before to remove sodium chloride. The toluenesolution was divided into three equal portions, and each portion wasworked up as described below.

Portion 1: A first portion of the toluene solution was concentrated atreduced pressure over several hours while keeping the liquid temperaturebelow 55° C., and the resulting dark oil stored in a refrigerator for 61days. During this time, the oil darkened and became more viscous. GCanalysis (OV 1701, 80° C., 0 hold time, 16° C./min. to 280° C.)indicated loss of more than 60% of the monomer. The major decompositionproduct appeared to be polymeric. Attempts to polymerize the monomer asdescribed in Example 8 were discontinued when large amounts of tarrymaterial precipitated upon adding the divinylbenzene and styrenemonomers to the dark viscous oil.

Portion 2: A second portion of the toluene solution was dried overanhydrous sodium sulfate, after which anhydrous hydrochloric acid wasadded through a bubbler to the stirred and cooled solution. The whitesolid (the hydrochloride salt of N-vinylbenzyl-N-(bis)2-picolylamine)that formed was filtered, washed with fresh toluene and air dried atroom temperature. The white solid was stored for 61 days at roomtemperature without any visible changes in appearance or its infraredspectrum. The acid salt of the monomer was dissolved in water, treatedwith aqueous base, and extracted as in Example 2 to give the monomer inits free base form. Polymerization as described in Example 9 gave theexpected polymer.

Portion 3: A third portion of the toluene solution was extracted withtwo portions of 5% aqueous hydrochloric acid and the acidic layerscontaining the acid salt of N-vinylbenzyl-N-(bis)2-picolylamine werecombined and stored in a refrigerator. At the end of 64 days, theaqueous layer was decanted from some tarry material that had formed,made basic with aqueous sodium hydroxide, and extracted with threeportions of toluene. The organic layers were combined and concentratedat reduced pressure over several hours while keeping the liquidtemperature below 55° C. GC analysis (OV only 1701, 80° C., 0 hold time,16° C./min. to 280° C.) indicated loss of about 25% of the monomer. Themajor decomposition product appeared to be the tarry polymeric materialformed in the aqueous solution of the acid salt. The monomer isolatedwas polymerized as described in Example 9 to give the desired polymer.

Similar surprising and improved stability was observed for the acidsalts of N-vinylbenzyl-N-2-picolylamine andN-vinylbenzyl-N-2-(2-pyridylimidazoline).

What is claimed is:
 1. A selective chelating resin comprising repeatingunits derived from a polymerizable monomer having the formula: ##STR4##wherein R=(CH₂)_(n) -Py wherein n=1 to 3 and Py=a pyridyl group; andR²=H, a C₁ to C₁₂ alkyl group, optionally hydroxyalkyl, or, independently,another group of the formula R¹.
 2. A selective chelating resinaccording to claim 1 which is characterized by the suspensionco-polymerization of the polymerizable monomer with styrene anddivinylbenzene.
 3. A selective chelating resin according to claim 1 inwhich the polymerizable monomer is selected from the group consistingof:N-vinylbenzyl-N-(bis)2-picolylamine; N-vinylbenzyl-N-2-picolylamine;1-vinylbenzyl-2-(2-pyridyl)imidazole;N-vinylbenzyl-N-2-hydroxyethyl-N-2-picolylamine; andN-vinylbenzyl-N-2-hydroxypropyl-N-2-picolylamine.
 4. A selectivechelating resin according to claim 2 in which the polymerizable monomeris selected from the group consistingof:N-vinylbenzyl-N-(bis)2-picolylamine; N-vinylbenzyl-N-2-picolylamine;1-vinylbenzyl-2-(2-pyridyl)imidazole;N-vinylbenzyl-N-2-hydroxyethyl-N-2-picolylamine; andN-vinylbenzyl-N-2-hydroxypropyl-N-2-picolylamine.
 5. A selectivechelating resin according to claim 1, wherein R² =H.
 6. A selectivechelating resin according to claim 1 wherein R² =a C₁ to C₁₂ alkyl orhydroxyalkyl group.
 7. A selective chelating resin according to claim 1wherein R² is, independently, another group of the formula R¹.
 8. Aselective chelating resin according to claim 1, wherein n=1 and Py=a2-pyridyl group.
 9. A selective chelating resin according to claim 8,wherein R² =H.
 10. A selective chelating resin according to claim 8,wherein R² =a C₁ to C₁₂ alkyl group or hydroxyalkyl group.
 11. Aselective chelating resin according to claim 10, wherein R² is ahydroxyethyl or hydroxypropyl group.
 12. A selective chelating resinaccording to claim 11, wherein R² is a 2-hydroxyethyl group or2-hydroxypropyl group.
 13. A selective chelating resin according toclaim 8, wherein R² is, independently, another group of the formula R¹.14. A selective chelating resin according to claim 13, wherein n=1 ineach of R¹ and R².
 15. A selective chelating resin according to claim14, wherein Py is a 2-pyridyl group in each of R¹ and R².